Electron tube variable impulse communication system



Oct. 19, 1948. R. E. MUMMA ETAL ELECTRON TUBE VARIABLE IMPULSE COMMUNICATION SYSTEM Filed Feb. 25, 1943 l4Sheets-Sheet 1 Their Attorney d n m m Q mm m S? m m\\ m m m W m m y n B 1 w\\ m Q m \N\ n A P D m QQ\\ QQ\ \Q\ Q- NS mQ m .r 5 m PNQ w? Oct. 19, 1948. R. E. MUMMA ETAL 2,451,859

ELECTRON TUBE VARIABLE IMPULSE COMMUNICATION SYSTEM Filed Feb. 25, 1943 14 Sheets-Sheet 2 Robrn E. Mumma and Franris X. Bucher cq R Inventor:

Their Attornev Oct. 19, 1948.

Filed Feb. 25, 1943 R. E. MUMMA ETAL ELECTRON TUBE VARIABLE IMPULSE COMMUNICATION SYSTEM 14 Sheets-Sheet 3 Robert E. Mummn and Francis X. Buchcr Inventors Their Attorney Oct. 19, 1948. R. E. MUMMA EI'AL ELECTRON TUBE VARIABLE IMPULSE COMMUNICATION SYSTEM Filed Feb. 25, 1943 14 Sheets-Sheet 4 All Robert E. MIII'III'III and Francis X Buchcr Inventor:

Their Attorney a m a m u n \J x w x W m AI AI. V u w W fr Av m Av A A W m A" I HMAW A" 4 "v Oct. 19, 1948. R. E. MUMMA ET AL 2,451,359

ELECTRON TUBE VARIABLE IMPULSE CQHMUNICATION SYSTEM Filed Feb. 25, 1943 14 Sheets-Sheet 5 Robcn E. Mum: and

Francis X. Bucha- Inventors Their Attorney 1948- R. E. MUMMA ETAL 2,451,359

ELECTRON TUBE VARIABLE IMPULSE COMMUNICATION SYSTEM Filed Feb. 25, 1943 14 Sheets-Sheet 6 FIG-.6

Robert E. Mum and Francis X. Bucher Inventor:

Their Attorney Oct. 19, 1948. R. E. MUMMA ETAL ELECTRON TUBE VARIABLE IMPULSE COMMUNICATION SYSTEM 14 Sheets-Sheet 7 Robert E. Mum: and

Francis X Buchcr Inventor! BY M M Their Attomev 1 RME NM b hm QL Q n H 3 h J q. I d "Em ngmm 0% .6...-

1943' R. E. MUMMA ETAL 2,451,859

ELECTRON TUBE VARIABLE IMPULSE COMMUNICATION SYSTEM Filed Feb. 25, 1943 14 Sheets-Sheet 8 Robert E. Mumma and Francis X Buchcr Inventor- M M mnmw Their Attorney Oct. 19, 1948.

R. E. MUMMA ETAL 2,451,859

ELECTRON TUBE VARIABLE IMPULSE COMMUNICATION SYSTEM Filed Feb. 25, 1943 14 Sheets-Sheet 9 Robert E. Mumml and Francis X. Buchcr lnvnntorl Thoh' Attorney Oct. 19, 1948. R. E. MUMMA ETAL 2,451,859

ELECTRON TUBE VARIABLE IMPULSE COMMUNICATION SYSTEM Filed Feb. 25. 194;: 14 Sheets-Sheet 10 U 1 AAA- All.

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Oct. 19, 1948- R. E. MUMMA ETAL 2,451,359

ELECTRON TUBE VARIABLE IMPULSE COMMUNICATION SYSTEM Filed Feb. 25, 1943 14 Sheets-Sheet 12 Robert E. Mumma and Francis X. Buchcr Inventors Their Attornev 1948- R. E. MUMMA EI'AL 2,451,359

ELECTRON TUBE VARIABLE IMPULSE COMMUNICATION SYSTEM Filed Feb. 25, 1943 14 Sheets-Sheet 13 Q y FIG.13

Their Attorney Oct. 19, 1948. R. E. MUMMA ETAL ELECTRON TUBE VARIABLE IMPULSE COMMUNICATION SYSTEM 14 Sheets-Sheet 14 Filed Feb. 25, 1943 Robml. Mumma and Francis X. Buchcr Inventor:

Their Attorney Ir- LI 7 TI WW m m? m w m DII D I A V DD, N J A1 4111 AI (I14 l fia lx M" n "a QM C MI w 3 (K m v J Q. A F A P A P 1 A F 1 4 4 3V1 Qu VF 0E Qmw 9% Q 3 3% Patented Oct. 19, 1948 UNITED STATES PATENT OFFICE ELECTRON TUBE VARIABLE mill-8E COMMUNICATION SYSTEM Application February 25, 1943, Serial No. 477,096

8 Claims. (Cl. 177-353) This invention relates to communication systems and is directed particularly to a system in which data is transmitted in the form of bursts of dlflerent numbers of substantially identical signals.

In the instant system, each of the several symbols that may be transmitted is transformed into a burst or train containing an assigned predetermined number of substantially identical signals having like significance. Accordingly, it is the number of signals in a burst by which each symbol is represented and not the variations in the signals, per se, which make up the bursts. Under these conditions, the signals used to transmit the data can be so chosen that slight variations which might occur in the signals during transmission will not be eilective to cause errors in the reception of this data. Applicants, therefore, by their novel system and means employed therein, have provided a reliable communication system in which slight variations in signals during transmission are not effective to cause erroneous reception of the data.

A sending station is provided with means for transforming the symbols into bursts of signals and generating the number of signals required in each burst accordin to the symbols being sent. The signals by which the symbols may be represented may take any desired form; for instance, they may consist of discrete rapidly recurring impulses and/or interruption or modulation of a continuous carrier wave. The signals can be transmitted from the sending station to a receiving station in any desirable manner, as, for instance, over a wire or by radio.

The bursts of signals representing the different symbols to be transmitted are sent one after another over a single communication channel, with a predetermined time interval or space be tween the bursts. The signals in the various bursts are used to cause the operation of means at the receiving station to set up direct representations oi the symbols, and the spaces between successive bursts of signals are used to enable means at the receiving station to generate control signals which control routing means at the receiving station to govern the allocation and storage of the symbols in the means for setting up direct representations oi the symbols.

The means for setting up direct representations of the symbols at the receiving station consists of a plurality of transforming and symbolstoring means, each being formed from a group of devices which represent the symbols. The

transforming and symbol-storing means are selectively and successively rendered eiiective by the routing means under control of the control signals. and. when any one of these means is eiiective. the devices therein are diflerentially operated according to the number of signals in a burst to transform the signals back into a single representation of the symbol and to store this representation.

The apparatus at the receiving station responds to the signals when they are received, and, since it is the number of signals and not their position in a fixed cycle which is the controlling factor, there is no need to synchronize the operation of the apparatus at the sending and receiving stations either before or during a transmitting operation.

Reliable high-speed communication of data is obtained with applicants novel arrangement because apparatus at the sending and receiving stations can generate and respond to the signals at a high frequency and because the signal bursts, which are used to represent the various symbols, are made up of signals having like signiiicance, require only the time necessary to produce the number of signals needed to represent the symbols, and can follow one after the other in transmission without unnecessary loss of time between bursts.

so Furthermore, there is no particular sequential relation between the various symbols and the number of signals which may be used to represent them, so that the number of signals which are assigned to represent any symbol may be chosen arbitrarily, Because of this condition, the symbols used most frequently can be represented by the smaller number oi signals, and this will also reduce the time required for the communication of data.

It is an object of the invention, therefore. to provide a novel communication system in which variations in the signals, per se, during their transmission do not produce erroneous results in the reception of the signals.

A further object of the invention is to provide a novel high-speed means for sending and receiving data in the form of bursts of different numbers of substantially identical signals.

A further object of the invention is to provide a means for producing bursts of signals, each burst comprising a predetermined numbler of signals of equal amplitude and the several bursts being separated by uniform time intervals.

A further object of the invention is to provide 55 a means upon which may be set a plurality oi symbols comprising data to be transmitted. which symbols are transformed one after another into bursts of diflerent numbers of substantially identical discrete signals representing the symbols and are sent out at spaced intervals over a single communication channel.

A further object of the invention is to provide a receiving apparatus which is not attested by variations in signals which might occur as they are transmitted thereto.

A further object of the invention is to provide means for receiving different numbers of similar discrete signals which represent symbols and transforming the diiierent numbers of signals into representations of the symbols.

A further object of the invention is to provide a receiving apparatus for receiving bursts of impulses, which receiving apparatus contains means to generate a control signal after each burst of impulses has been received.

A further object of the invention is to provide a receiving apparatus for receiving and transforming bursts of different numbers of symbolrepresenting signals into single representations of the symbols, said receiving apparatus containing a plurality of transforming means for setting up said single representations of various symbols according to the number of signals in a burst,

means for generating a control signal after each burst of symbol-representing signals has been received, and routing means operated by the control signals to route the different bursts of signals to different ones of the transforming means.

With these and incidental objects in view, the invention includes certain novel features of construction and combinations of parts, the essential elements of which are set forth in appended claims and a preferred form or embodiment of which is hereinafter described with reference to the drawings which accompany and form a part of this specification.

In the drawings:

Fig. 1 shows the portion of a set of keys for setting up a symbol in the sending apparatus and a portion of the symbol-transforming means controlled thereby for generating the number of impulses which will be sent to represent the symbol set up on the keys.

Figs. 2 to 5 inclusive are similar to Fig. l and together with Fig. 1 provide means for setting up and generating the signals to represent five symbols in succession.

Fig. 6 shows the start and stop controls for the sending apparatus and also shows the means for amplifying and sharpening the impulses which have been generated to represent the several symbols.

Fig. '7 shows the means for receiving the bursts of impulses and for creating an impulse to control a routing means after each burst is received.

Figs. 8 to 12, inclusive, show portions of the transforming and symbol-storing means in the receiving apparatus, which means consist of groups or banks of symbol-representing tubes which may be selectively set according to the symbols corresponding to the impulses sent by the sending apparatus.

Fig. 13 shows relay means for selectively directing or routing impulses to the various groups of transforming and symbol-storing means.

Fig. 14 shows a routing control device containing a plurality of sequentially operable tubes which are operated by the control signals to control the relay means which route the impulses representing various symbols into the proper Broups or banks of transforming and symbolstoring means.

GENERAL DECRIPTION The symbols which may be sent and received by the novel apparatus may represent any selected data such as the digits of numerical notation, the letters of the alphabet, or any other arbitrary data which may be chosen.

The disclosed embodiment is shown with a capacity for automatically transmitting flve symbols in succession and is arranged to transmit the digits 0 to 9 inclusive of a numerical notation.

For the purposes of this disclosure, the signals by which the symbols are represented will consist of discrete rapidly recurring negative impulses of substantially uniform amplitude, and these impulses will be transmitted from the sending apparatus to the receiving apparatus over a wire. However, it is not intended to limit the invention to this particular form of signal and transmission medium, as the invention is capable of being carried out by using other equivalent arrangements.

The sending apparatus contains five groups or banks of keys. The keys of each group represent the symbols for the digits 1 to 9 inclusive and are used for setting up symbols to be transmitted. Associated with each bank of keys is a bank of aseous electron tubes which contains a tube corresponding to each symbol represented by the keys, and, in addition to these tubes. contains a tube corresponding to the "0 symbol, and a shift tube.

The tubes of each bank are connected in a chain to be fired automatically one after another in sequence from the 9" tube through the "0 tube, and. as they are fired, they generate the impulses which make up the burst. The depressed key in any bank selects the starting point in the firing sequence by preparing its related symbolrepresenting tube to be fired in response to an impulse commonly impressed on all of the symbolrepresenting tubes; however, if no key is depressed ln the bank, the 0" tube is prepared and will be flred by the impulse. Once a tube in a bank is tired, it will start the automatic firing of the other tubes in the sequence one after another until the shift tube is tired and becomes conducting. By means of these tubes, the symbol is transformed into a series of rapidly recurring impulses. The symbol-representing tubes are connected to an impulse line and send an impulse over the line each time one of the tubes is fired, and these impulses are amplified and sharpened and sent as substantially equal-amplitude impulses to the receiving apparatus.

When the last symbol-representing tube in a chain is tired, it causes the shift tube of this bank to be iired and send an impulse to the symbolrepresenting tubes of the next bank of tubes to fire the prepared symbol-representing tube therein and start the sequential firing of the tubes of that bank. By means of the shift tubes, various banks oi tubes are rendered operative one after another in succession and enable the impulses representing the difl'erent symbols to be sent in succession over a single communication channel. The output from these generating tubes will therefore consist of a plurality of bursts of rapidly recurring equal-amplitude impulses, one burst of impulses for each bank of tubes.

After the keys in the various banks have been set according to the symbols to be transmitted, the transmission of the symbols is initiated by the operation of a start key, which causes a tiring impulse to be sent to the symbol-representing tubes oi the first bank of tubes to start the sequential firing of the tubes therein. The remaining banks of tubes will be rendered operative automatically in succession, and the shift tube of the last bank will cause the termination of the transmitting operation.

The receiving apparatus contains means upon which the received impulses are impressed and which is capable of causing a control impulse to be generated after each burst of impulses: a routing means operated by the control impulses: and a plurality of transforming and symbol-storing means each consisting of a group or bank of gaseous electron tubes for transforming one of the bursts of impulses into a single representation of the symbol and storing the symbol.

Each group or bank of transforming and symbol-storing tubes contains a tube representing each symbol, and a presetting tube. The symbolrepresenting tubes of each bank are connected to be fired one after another in response to the impulses sent out by the sending apparatus, the order firing beginning with the "0 tube and continuing through the tubes "1" to "9, in that order, which, it will be noted, is exactly the reverse order of the firing of the tubes in the sending apparatus. As each tube in the bank is fired, it extinguishes any previously conducting tube in the bank, and this means that only one tube will be conducting in each bank at the end of a receiving period and these conducting tubes in the various banks will correspond to the symbols received. The conducting tubes will continue to conduct after the receiving period and serve as a means for storing the symbols.

As explained earlier herein, the bursts of 1mpulses representing the various symbols are sent out one after another in succession over a single wire, and, because of this, routing means must be provided in the receiving apparatus to distribute or allocate the bursts to the proper banks of transforming and storing tubes. The particular routing means shown herein includes a normally inoperative relay means for each bank of tubes, which relay means may be selectively rendered effective one after another to relay the bursts of impulses from a common impulse conductor in the receiving apparatus to the various banks of transforming and symbol-storing tubes.

The relay means are rendered effective one after another by means of a routing control device consisting of a series of gaseous electron tubes which are connected in a chain to be fired and rendered conducting one after another in sequence in response to the control impulses. The tubes of the routing control device are also connected so that the firing of any tube in thechain will cause any previously conducting tube of the chain to be extinguished and allow only one tube at a time to be conducting. The chain connections and extinguishing connections between the routing control tubes, therefore, enable the tubes to become conducting one at a time in sequence. and, as long as any tube is conducting, it renders its associated relay means operative to relay impulses from the common impulse conductor to its associated bank of transforming and symbol-storing tubes. While the routing means is shown as consisting of a plurality of relays, it is obvious that the routing means could consist of a commutator or a sequence switch which is capable of step-by-step operation to relay the impulses to the various banks.

The means upon which the received impulses 6 areimpressedpassestheseimpulsestothe common impulse conductor in the receiving apparatus, from which conductor the impulses are relayed selectively to the various banks of transforming and symbol-storing tubes by the several relays of the routing means. The means upon which the received impulses are impressed is also effective to control a control impulse generating means in the receiving apparatus to cause an impulse to be generated after each burst of impulses has been received.

The control impulses which are generated in the receiving apparatus are impressed on the routing control tubes to cause different ones 0! these tubes to be fired after the various bursts of impulses have been received in the receiving apparatus.

The operation of the receiving apparatus is as follows:

The receiving apparatus is prepared for the reception of data by causing the presetting tube of each bank of transforming and symbol-storing tubes and the first tube in the routing control device to be fired and rendered conducting.

The firing of the presetting tube in each bank of transforming and symbol-storing tubes will. through the mutual extinguishing connections. clear these banks of any previously stored symbols, and the firing oi the first tube in the routing control device will likewise cause any other tube of the device to be extinguished and insure that the first entry will always be routed to the first bank of transforming and symbol-storing tubes.

The conducting presetting tube of each bank will prepare the 0" tube in its bank of tubes to be responsive to signal impulses and will continue to be conducting until symbol-representing signal impulses are relayed to that bank and cause the 0" tube therein to be fired and rendered conducting.

The conducting routing control tube renders the relay means for the first bank effective and prepares the routing control tube for the second bank for firing in response to the first control impulse to be generated.

The receiving device is now ready to receive signals. As the first burst of impulses is received. these impulses will be passed on to the common impulse conductor and relayed from the common impulse conductor to the first bank of transforming and symbol-storing tubes, and these tubes will be operated one after another in response to these impulses. the last tube to be operated being the symbol-representing tube corresponding to the symbol represented by the burst. After the first burst of impulses has been received, the control impulse generating means operates and sends an impulse to the routing control tubes. The routing control tube for the second bank has been prepared for firing by the conduction in the first tube, and, when the impulse is sent to these tubes by the control impulse generating means, the second bank routing control tube is fired and rendered conducting.

The second bank routing control tube, when it is fired, causes the first bank routing control tube to be extinguished, and thereby the first bank relay means to return to its normal inoperative state: prepares the third bank routing control tube for operation in response to the next control impulse; and renders the relay means for the second bank of transforming and symbol-storing tubes operative.

The next burst of impulses will cause the transforming and symbol-storing tubes of the second bank to be fired to set up and store the symbol represented by the second burst oi impulses. As before, a control impulse is generated after this burst is received, and will cause the firing of the next routing control tube to prepare the next transforming and symbol-storing bank for the reception of the next burst of impulses. In this way. the successive bursts of impulses are routed to the various banks of transforming and symbolstoring tubes and control the setting of the various symbols therein.

After the sequence of bursts has been received, the conducting tubes representing the symbols in the various banks can be used to control an indicating means or a recording means or can be used to control the transfer of the symbols directly to other storing means for future use.

The invention is not limited to the use of a multiple-bank sending apparatus, because a single bank could be used repeatedly to send out successive bursts of impulses which the receiving apparatus would allocate and transform into successive settings representing the sy bols in the same manner as explained above for the five-symbol sequence. Nor is the receiving apparatus limited to live banks of transforming and symbolstoring tubes, as it is obvious that more banks of transforming and storing tubes could be used if it were desired to increase the capacity of the receiving apparatus.

Thus it is seen that applicants have provided a novel system and means for reliably communieating data over a single communication channel at a. high rate of speed.

DETAILED DESCRIPTION Bnuinrc Assess-ms The sending apparatus is shown in Figs. 1 to 6 inclusive.

The disclosed embodiment of the invention is adapted to send five symbols automatically in succession in the form of bursts of impulses having substantially the same amplitude. which bursts contain different numbers of these impulses, depending upon the particular symbols represented thereby. The burst by which the symbol is represented contains one impulse; the burst for the symbol 1" contains two impulses; and the burst for the symbol 2 contains three impulses. This relation between the number of impulses and the symbols which they represent extends to the symbol "9," which is represented by ten impulses: however, the invention is not limited to this particular relation between the symbols and the numbers of impulses assigned thereto, as any desired number of impulses can arbitrarily be assigned to represent any symbol.

In the following description, the numerals "I." III," "IV," and "V" indicate the order in which the symbols are transmitted, and similar numerals will be applied to the parts of the apparatus which take part in the transmission or these symbols.

Symbobtmnsjormina means Five banks of keys are provided for setting up the symbols, and associated with each bank is a symbol-transforming means which generates the different numbers of impulses by which the symbols are represented. The banks are shown in Figs. 1 to 5. inclusive. and. as the banks are substantially alike, it is believed that the operation of all the banks will be clear from a description of the elements of one bank and their operation.

In this disclosure. the values of the various applied potentials are given with reference to Bround. It is not intended that the invention be limited to the use of the particular potentials and values of resistance and capacitance given in the following description, because the potentials applied to the various elements of the tubes are merely selected as convenient potentials for the disclosure, and the circuit elements of resistance and capacitance correspond in relative value to the potentials chosen. It is obvious that other potentials may be used and the values of the circuit elements adjusted accordingly to maintain the proper relation between the various parts of the circuit. Throughout the drawings, the cathode heater elements are shown conventionally.

Referring to Fig. 1, which shows a symboltransforming means for the first symbol to be transmitted, it will be seen that the symboltransforming means is made up of a plurality of gaseous electron tubes. These tubes are of the type having an internal potential drop of about 15 volts when conducting, and having an anode, a cathode, and a control grid which is given a negative bias with respect to the cathode and will prevent the tube from firing until this bias is reduced to less than 15 volts negative with respect to the cathode.

As many symbol-representing tubes will be included in each bank as there are symbols which may be selected for transmission, and these tubes will generate the diflerent numbers of impulses by which the symbols are represented. In the present embodiment, each group will include a tube for the symbols for the digits 0" to 9." though in Fig. i only the 0, and 9" tubes are shown, the symbol-representing tubes for the digits "4 to 7" inclusive having been omitted to simplify the showing of the bank because the circuits for these tubes are identical with those of other symbol-representing tubes and the operation of the symbol-transforming means can be readily understood without a showing of them.

One shift tube Shift" is provided for the bank and is operated to shift the control of the sending of impulses, from one bank to another, by impressing a starting impulse on another bank to start the sending of another burst of impulses after the last symbol-representing tube of one bank has operated to generate the last impulse in the burst of the symbol-representing impulses.

The circuits for supplying potential to the elements of the symbol-representing tubes and for interconnecting these tubes for sequential operation are similar for all these tubes and will be clear from the explanation of the circuits shown.

Negative potential is supplied to the cathodes of the symbol-representing tubes by means of parallel circuits, one for each tube, extending to ground from a negative potential supply conductor "II, to which a negative potential of volts is applied at terminal iill. The circuit for the "1 tube is representative and extends from the supply conductor Hill at point I03 over resistor ll" of 150,000 ohms. point I05, a. resistor I00 of 75,000 ohms, points I07 and I08, and over resistor I00 of 15,000 ohms and capacitor H0 of .002 microfarad in parallel. to ground.

The cathode III of the "1" tube is connected to this circuit at point I01 and has a negative potential of approximately 9 volts when the tube is not conducting. When the tube is conducting, the Cathode is also conductlvely coupled to its related anode by the discharge path through the tube, so that the positive potential which is applied to the anode will also be impressed on the cathode potential supply circuit and will cause the potential or the cathode to rise irom a negative potenial of 9 volts to a positive potential oi about 70 volts.

Each cathode potential supply circuit is utilized to supply negative biasing potential for the control grid of the next tube in the sequence, which is, in this case, the tube. From the point I00 in the cathode potential supply circuit for the 1" tube, a connection extends through point 2, over resistor Ill of 500,000 ohms, point ill, resistor H0 0! 50,000 ohms, to the control grid N0 of the 0" tube and provides this grid with a negative biasing potential of approximately 56 volts. This connection between the cathode potential supply circuit of one tube and the control grid of the next adjacent tube of the series enables the potential rise of the cathode of one tube to reduce the bias of the control grid 0! the next tube in the sequence to a value below its critical potential and will cause the next tube to automatically tire and become conducting.

Since the "9" tube is the first tube in the sequence, the control grid I ll of this tube is given a biasing potential of the same value as the grids of the other tubes by means of a circuit which is equivalent to the other cathode potential supply circuits and extends from the negative potential supply conductor I00 at point IIO, over resistor "0 of 150,000 ohms, point I 20, and resistor I2I of 90,000 ohms to ground, to which circuit the grid I I1 is connected from point I20 over resistor I22 of 500,000 ohms, point I20, and resistor I20 of 50,000 ohms.

Each control grid of the symbol-representing tubes is electrostatically connected to a firing impulse conductor I00, the connection for the grid 0 or the 0" tube extending from point Ill in the grid circuit, over a capacitor III of micromicroiarads to the conductor I00. The firing impulses, which are positive potential impulses impressed on conductor I00, tend to reduce the negative bias of the control grids below their critical value, but are not suincient to overcome the normal negative bias. The firing impulse will be eiiective to cause a tube to be fired only if that tube has been "prim or has its grid bias reduced to near the critical point so that the firing Impulse can reduce the bias below its critical point and cause the tube to fire and become conducting. The

manner in which the tubes can be primed" will be explained hereinafter.

Positive potential is supplied to the anodes of the symbol-representing tubes by a circuit which extends from terminal I02 (Fig. 0), upon which is impressed a positive potential oi 105 volts. and continues over conductor I00, point I00, conductor I00, a resistor I00 0! 250 ohms, point I01, a resistor I00 of 3,000 ohms, point I00, and conductor I00 to the common anode potential supply terminal III for the symbol-representing tubes.

Point I01 in this circuit is connected to ground over a capacitor of 0 microi'ara/ds, which capacitor absorbs the shock of any abrupt potential application or change in the circuit.

Terminal Ill is connected to terminal I" (Fig. 1), to which is connected an anode potential supply conductor Ill for the symbol-representing tubes of this bank. Each of the anodes oi the symbol-representing tubes 01' this bank is connected over a resistor of 1.000 ohms to the anode potential supply conductor I, as, to: instance,

10 resistor I, over which the anode I00 0! the "1 tube is connected to the anode potential supply conductor I40.

when none of the symbol-representing tubes is conducting, a positive potential of volts is applied to the anodes: however, when one oi these tubes is conducting, the potential will be reduced to about 85 volts due to the drop across the resistors I00, I00, and I.

At the moment one of these tubes is tired, its cathode will remain at a negative potential of 9 volts, while the capacitor, as I I0, is charging, and, due to the resistance in the common anode potential supply circuit for the symbol-representing tubes and the internal potential drop of the tube, the potential of the anode will drop to within about 15 volts of the cathode potential. This will cause a drop in potential of the anode potential supply conductor I43, which drop provides a negative potential impulse on the conductor. As the anodes of all the symbol-representing tubes oi a bank are connected to the anode potential supply conductor I 00, a series of negative impulses will occur on the conductor as these tubes are fired one after another. These impulses are sent to the receiving apparatus after they have been amplified and sharpened.

The drop in the potential of the anode potential supply conductor III is also used to extinguish any previously conducting tube which has its anode connected to the common source of anode potential for the symbol-representing tubes, which includes the resistors I30 and I30. The extinguishing action occurs because the potential of all the anodes of these tubes will drop as the potential of the anode supply conductor I03 drops, and this will cause the potential of the anode of a previously conducting tube to drop below the potential of its cathode, which has risen due to conduction in the tube, and will cause conduction to cease in that tube and enable the control grid to regain control.

, Cathode IOI of the shift tube is normally supplied with a negative potential of approximately 9 volts by being connected at point I02 in a circuit extending from point I00 on the negative potential supply conductor I00, over resistor I04 0! 390,000 ohms, point I05, point I02, and to ground over resistor I00 of 25,000 ohms in parallel with resistor I0I oi 2,500 ohms in series with capacitor I00 of .002 microfarads. when the shiit tube fires and becomes conducting, the potential of the cathode IOI will rise to a positive potential of about volts, and this potential rise is used as a firing impulse to start the sequential firing of the tubes in bank II.

The control grid I00 oi the shift tube obtains its negative bias from the cathode potential supply circuit for the "0" tube. The connection is from point I00 in the cathode potential supply circuit oi the 0 tube and over point IOI and resistor I02 of 500,000 ohms to the control grid I09. The potential rise of the cathode of the "0" tube, when that tube is conducting, is effective to reduce the negative bias on the control grid I09 and cause the shift tube to fire and become conducting. A capacitor I 00 of 3,000 micro-microfarads is connected between point IOI in this circuit and ground to delay potential rise oi the control grid I00 and the consequent iiring of the shift tube alter the firing of the "0" tube. This delay in the firing oi the shift tube provides a time interval between bursts, which interval may be made longer or shorter as desired by varying the capacity oi capacitor I00.

Potential is supplied to the anode I of the shift tube by a circuit which starts at the terminal I" (Fig. 6). which has a positive potential of 150 volts impressed thereon, and continues over conductor I", resistor ill 250 ohms, point I", and resistor III of 3,000 ohms to the common anode potential supply terminal I" for the shift tubes. Point I in this circuit is connected to ground over a capacitor oi 4 microtarads. Terminal I'll is connected to terminal I'll (Fig. 1), to which the anode ill of the shift tube is connected. As in the case of the anodes of the other tubes of the bank, the potential of the anode will drop to about volts above the potential of the cathode, while the capacitor I" is charging, and this potential drop will be efi'ective to extinguish any previously conducting tube which derives its anode potential over the resistors I61 and I" (Fig. 6) in the common anode potential supply circuit for the shift tubes. Since the anodes oi the symbol-representing tubes have a different anode potential supply circuit from that of the shift tubes. the firing of the shift tube will be inefiectlve to extinguish the "0" tube, which is the last symbol-representing tube in the bank to be fired. The "ll" tube, therefore. which is conducting at the end of an operation of the tubes of the bank, remains in this condition until the first symbol-representing tube of the next bank is fired.

The sequential and automatic firing oi the tubes of a bank always begins with a symbolrepresenting tube and is initiated by a firing impulse. As explained earlier herein, the control grids of the symbol-representing tubes are electrostatically connected to the firing impulse conductor I but are normally sufiiciently negatively biased so that a firing impulse impressed on the conductor will not be eii'ective to reduce the bias below its critical point to cause any 01' the tubes to be fired and rendered conducting. In order that a firing impulse will be efiective to fire a tube, the tube must be "primed" by having the normal bias of its grid reduced to such a degree that the flring impulse will be sufllcient to carry the bias below the critical value and cause the tube to tire and become conducting; accordingly, the selection of the tube with which the sequential operation of the tubes in the bank is to begin can be eflected by the selective "priming of the tubes. This is accomplished under control of the keys upon which the symbols may be set.

Fig. 1 shows schematically a portion of the row of keys upon which the first symbol to be transmitted may be entered. Only the keys for the digits 1, 2, "8, and 9" are shown. the keys for the digts "3" to "7" inclusive having been omitted to simplify the showing of the bank, inasmuch as the circuits controlled by the omitted keys are similar to the circuits shown and the operation of the keys to selectively prime the tubes can be understood from the circuits shown.

The keys of the bank are normally in an undepressed condition, and when in this position they complete a priming circuit to the 0" tube, which circuit starts at terminal I15, upon which a positive potential or I05 volts is -impressed, and continues over potential supply conductor I'll, point I'll, conductor I'll, key-controlled contacts, as I19, in series. and over conductor Ill and resistor I81 01' 300,000 ohms to point II! in the circuit to the control grid H. of the 0" tube.

when any key of this bank is depressed, it interrupts the priming circuit described above and closes a priming circuit from the potential supply conductor I'll to the control grid of its related symbol-representing tube. The "1" key I82 (Fig. 1) is shown depressed, interrupting the priming circuit to the0" tube at the point I" and completing a priming circuit to the control grid I of the "1" tube. The priming circuit for control grid I extends from point III on the potential supply conductor, over contact ll. of the depressed 1" key, conductor Ill, and over resistor ill of 300,000 ohms to point III in the circuit to control grid I.

The application of positive potential by this circuit to the control grid I of the "1" tube reduces the negative biasing potential of the control grid I almost to its critical point, and, when the firing impulse is impressed on the tubes, the bias of the control grid of the 1" tube will be reruced to within 15 volts negative with respect to the potential of the cathode, and the tube will fire and become conducting. In a similar manner, the closure of a priming circuit to any of the other symbol-representing tubes will select that tube to begin the sequential and automatic firing of the tubes of the bank.

The operation of the symbol-transforming means shown in Fig. l, by which the burst of impulses corresponding to the first symbol to be transmitted is obtained, will now be explained.

The key I82 corresponding to the digit "1" has been depressed to interrupt the priming circuit to the "0 tube and complete the primin circuit for the 1" tube. A firing impulse is impressed on the firing impulse conductor III and causes the firing of the 1" tube. At the moment the "1" tube is fired, its anode potential will drop because of the resistor Illand the resistors III and III in the symbol-representing tube anode potential supply circuit, causing a drop to occur on the conductor ill, terminal I", and terminal Ill (Fig. 6) of the anode potential supply circuit, which drop is amplified and sharpened to provide an impulse to be sent to the receiving apparatus. The potential of the cathode of the conducting "1 tube will rise and. through the connection between point I'll! in its potential supply circuit and the control grid H8 of the "0" tube, will cause the potential of the control grid III to rise and reduce the bias below its critical value and cause the "0 tube to fire and become conducting. The potential of the anode of the "0" tube will drop and cause another impulse on conductor I, terminal I42, and terminal ill in the anode potential supply circuit, which impulse will also be amplified and sharpened to provide another impulse to be sent to the receiving apparatus, and, in addition, the impulse on conductor I will also extinguish the conducting 1" tube. The potential of the cathode of the "0" tube will rise and cause the potential of the grid Ii! of the shift tube "Shift" to rise, reducing its bias below its critical value and causing the shift tube to fire and become conducting.

There is a predetermined delay in the potential change on the control grid III, due to the capacitor lit, which connects the point Iii in this circuit to ground. which delay provides the time interval or spacing between the successive bursts of impulses.

When the shift tube fires, there will be a potential drop in its common anode supply circuit. due to the resistors I61 and I. However, this drop will not be eiiective to extinguish the "0" tube, because its anode is included in a different anode potential supply circuit. The potential 

